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A display device (10) includes an upper substrate (first substrate) (2),
a lower substrate (second substrate) (3), and a conductive liquid (16)
that is sealed in a display space (S) formed between the upper substrate
(2) and the lower substrate (3) so as to be moved toward an effective
display region (P1) or a non-effective display region (P2). Ribs (14) are
provided on the lower substrate (3) so as to partition the inside of the
display space (S) in accordance with each of a plurality of pixel regions
(P). The height h of the ribs (14) in the direction perpendicular to the
upper substrate (2) and the lower substrate (3) is set to be smaller than
the gap size H of the display space (S) in the perpendicular direction.

1. A display device that comprises a first substrate provided on a
display surface side, a second substrate provided on a non-display
surface side of the first substrate so that a predetermined display space
is formed between the first substrate and the second substrate, an
effective display region and a non-effective display region that are
defined with respect to the display space, and a conductive liquid sealed
in the display space so as to be moved toward the effective display
region or the non-effective display region, and that is capable of
changing a display color on the display surface side by moving the
conductive liquid, wherein the display device comprises: a plurality of
signal electrodes that are placed in the display space so as to come into
contact with the conductive liquid, and are also provided along a
predetermined arrangement direction; a plurality of reference electrodes
that are provided on one of the first substrate and the second substrate
so as to be electrically insulated from the conductive liquid and to be
located on one of the effective display region side and the non-effective
display region side, and are also arranged so as to intersect with the
plurality of the signal electrodes; a plurality of scanning electrodes
that are provided on one of the first substrate and the second substrate
so as to be electrically insulated from the conductive liquid and the
plurality of the reference electrodes and to be located on the other of
the effective display region side and the non-effective display region
side, and are also arranged so as to intersect with the plurality of the
signals electrodes; a plurality of pixel regions that are located at each
of the intersections of the plurality of the signal electrodes and the
plurality of the scanning electrodes; and ribs that are provided on one
of the first substrate and the second substrate so as to partition an
inside of the display space in accordance with each of the plurality of
the pixel regions, and wherein a height h of the ribs in a direction
perpendicular to the first substrate and the second substrate is set to
be smaller than a gap size H of the display space in the perpendicular
direction.

2. The display device according to claim 1, wherein the ribs are provided
in the form of a frame so as to surround the corresponding pixel region,
and the height h of the ribs is set so as to satisfy the following
inequality (1): height h.ltoreq.0.9.times.(gap size H) (1).

3. The display device according to claim 2, wherein the height h of the
ribs is set so as to satisfy the following inequality (2):
0.65.times.(gap size H).ltoreq.height h (2).

4. The display device according to claim 1, wherein the ribs are provided
with clearances through which the adjacent pixel regions can communicate
with each other.

5. The display device according to claim 4, wherein the ribs include
first rib members formed in a direction perpendicular to a direction of
movement of the conductive liquid and second rib members formed in a
direction parallel to the direction of movement of the conductive liquid,
and the clearances are formed between each of ends of the first rib
members and the second rib members.

6. The display device according to claim 1, wherein the display device
comprises: a signal voltage application portion that is connected to the
plurality of the signal electrodes and applies a signal voltage in a
predetermined voltage range to each of the signal electrodes in
accordance with information to be displayed on the display surface side;
a reference voltage application portion that is connected to the
plurality of the reference electrodes and applies one of a selected
voltage and a non-selected voltage to each of the reference electrodes,
the selected voltage allowing the conductive liquid to move in the
display space in accordance with the signal voltage and the non-selected
voltage inhibiting a movement of the conductive liquid in the display
space; and a scanning voltage application portion that is connected to
the plurality of the scanning electrodes and applies one of a selected
voltage and a non-selected voltage to each of the scanning electrodes,
the selected voltage allowing the conductive liquid to move in the
display space in accordance with the signal voltage and the non-selected
voltage inhibiting a movement of the conductive liquid in the display
space.

7. The display device according to claim 1, wherein the plurality of the
pixel regions are provided in accordance with a plurality of colors that
enable full-color display to be shown on the display surface side.

8. The display device according to claim 1, wherein an insulating fluid
that is not mixed with the conductive liquid is movably sealed in the
display space.

9. The display device according to claim 1, wherein a dielectric layer is
formed on the surfaces of the plurality of the reference electrodes and
the plurality of the scanning electrodes.

10. The display device according to claim 1, wherein the non-effective
display region is defined by a light-shielding layer that is provided on
one of the first substrate and the second substrate, and the effective
display region is defined by an aperture formed in the light-shielding
layer.

11. An electric apparatus comprising a display portion that displays
information including characters and images, wherein the display portion
comprises the display device according to claim 1.

Description

TECHNICAL FIELD

[0001] The present invention relates to a display device that displays
information such as images and characters by moving a conductive liquid,
and an electric apparatus using the display device.

BACKGROUND ART

[0002] In recent years, as typified by an electrowetting type display
device, a display device that displays information by utilizing a
transfer phenomenon of a conductive liquid due to an external electric
field has been developed and put to practical use.

[0003] Specifically, such a conventional display device includes first and
second electrodes, first and second substrates, and a colored droplet
that is sealed in a display space formed between the first substrate and
the second substrate and serves as a conductive liquid that is colored a
predetermined color (see, e.g., Patent Document 1). In this conventional
display device, a voltage is applied to the colored droplet via the first
electrode and the second electrode to change the shape of the colored
droplet, thereby changing the display color on a display surface.

[0004] For the above conventional display device, another configuration
also has been proposed, in which the first electrode and the second
electrode are arranged side by side on the first substrate and
electrically insulated from the colored droplet, and a third electrode is
provided on the second substrate so as to face the first electrode and
the second electrode. Moreover, a light-shielding shade is provided above
the first electrode. Thus, the first electrode side and the second
electrode side are defined as a non-effective display region and an
effective display region, respectively. With this configuration, a
voltage is applied so that a potential difference occurs between the
first electrode and the third electrode or between the second electrode
and the third electrode. In this case, compared to the way of changing
the shape of the colored droplet, the colored droplet can be moved toward
the first electrode or the second electrode at a high speed, and thus the
display color on the display surface can be changed at a high speed as
well.

PRIOR ART DOCUMENTS

Patent Documents

[0005] Patent Document 1: JP 2004-252444 A

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

[0006] However, in the above conventional display device, pixel regions
are completely separated from one another by cavity partitions (ribs),
and the colored droplet (conductive liquid) is moved toward the first
electrode (non-effective display region) or the second electrode
(effective display region) in the internal space of each of the dosed
pixel regions. Therefore, it is difficult for the conventional display
device to improve the speed of movement of the colored droplet.

[0007] With the foregoing in mind, it is an object of the present
invention to provide a display device that can improve the speed of
movement of a conductive liquid, and an electric apparatus using the
display device.

Means for Solving Problem

[0008] To achieve the above object, a display device of the present
invention includes the following: a first substrate provided on a display
surface side; a second substrate provided on a non-display surface side
of the first substrate so that a predetermined display space is formed
between the first substrate and the second substrate; an effective
display region and a non-effective display region that are defined with
respect to the display space; and a conductive liquid sealed in the
display space so as to be moved toward the effective display region or
the non-effective display region. The display device is capable of
changing a display color on the display surface side by moving the
conductive liquid. The display device includes the following: a plurality
of signal electrodes that are placed in the display space so as to come
into contact with the conductive liquid, and are also provided along a
predetermined arrangement direction; a plurality of reference electrodes
that are provided on one of the first substrate and the second substrate
so as to be electrically insulated from the conductive liquid and to be
located on one of the effective display region side and the non-effective
display region side, and are also arranged so as to intersect with the
plurality of the signal electrodes; a plurality of scanning electrodes
that are provided on one of the first substrate and the second substrate
so as to be electrically insulated from the conductive liquid and the
plurality of the reference electrodes and to be located on the other of
the effective display region side and the non-effective display region
side, and are also arranged so as to intersect with the plurality of the
signal electrodes; a plurality of pixel regions that are located at each
of the intersections of the plurality of the signal electrodes and the
plurality of the scanning electrodes; and ribs that are provided on one
of the first substrate and the second substrate so as to partition the
inside of the display space in accordance with each of the plurality of
the pixels regions. A height h of the ribs in a direction perpendicular
to the first substrate and the second substrate is set to be smaller than
a gap size H of the display space in the perpendicular direction.

[0009] In the display device having the above configuration, the height h
of the ribs is set to be smaller than the gap size H of the display space
in the perpendicular direction. Thus, unlike the conventional example, a
clearance can be created between the other of the first and second
substrates and the ribs, so that the speed of movement of the conductive
liquid can be improved.

[0010] In the above display device, the ribs may be provided in the form
of a frame so as to surround the corresponding pixel region, and the
height h of the ribs may be set so as to satisfy the following inequality
(1):

height h.ltoreq.0.9.times.(gap size H) (1).

[0011] In this case, the speed of movement of the conductive liquid can be
reliably improved.

[0012] In the above display device, it is preferable that the height h of
the ribs is set so as to satisfy the following inequality (2):

0.65.times.(gap size H).ltoreq.height h (2).

[0013] In this case, the conductive liquid can be reliably prevented from
entering the adjacent pixel regions.

[0014] In the above display device, the ribs may be provided with
clearances through which the adjacent pixel regions can communicate with
each other.

[0015] In this case, due to the presence of the clearances, the conductive
liquid can be moved smoothly, and thus the speed of movement of the
conductive liquid can be improved.

[0016] In the above display device, the ribs may include first rib members
formed in a direction perpendicular to the direction of movement of the
conductive liquid and second rib members formed in a direction parallel
to the direction of movement of the conductive liquid, and the clearances
may be formed between each of the ends of the first rib members and the
second rib members.

[0017] In this case, the clearances are provided in four corners of each
of the pixel regions, and due to the presence of these clearances, the
conductive liquid can be moved smoothly, and thus the speed of movement
of the conductive liquid can be improved.

[0018] In the above display device, it is preferable that the display
device includes the following: a signal voltage application portion that
is connected to the plurality of the signal electrodes and applies a
signal voltage in a predetermined voltage range to each of the signal
electrodes in accordance with information to be displayed on the display
surface side; a reference voltage application portion that is connected
to the plurality of the reference electrodes and applies one of a
selected voltage and a non-selected voltage to each of the reference
electrodes, the selected voltage allowing the conductive liquid to move
in the display space in accordance with the signal voltage and the
non-selected voltage inhibiting a movement of the conductive liquid in
the display space; and a scanning voltage application portion that is
connected to the plurality of the scanning electrodes and applies one of
a selected voltage and a non-selected voltage to each of the scanning
electrodes, the selected voltage allowing the conductive liquid to move
in the display space in accordance with the signal voltage the
non-selected voltage inhibiting a movement of the conductive liquid in
the display space.

[0019] In this case, a matrix-driven display device with excellent display
quality can be easily provided, and the display color in each of the
pixel regions can be appropriately changed.

[0020] In the above display device, the plurality of the pixel regions may
be provided in accordance with a plurality of colors that enable
full-color display to be shown on the display surface side.

[0021] In this case, the color image display can be performed by moving
the corresponding conductive liquid properly in each of the pixels.

[0022] In the above display device, it is preferable that an insulating
fluid that is not mixed with the conductive liquid is movably sealed in
the display space.

[0023] In this case, the speed of movement of the conductive liquid can be
easily improved.

[0024] In the above display device, it is preferable that a dielectric
layer is formed on the surfaces of the plurality of the reference
electrodes and the plurality of the scanning electrodes.

[0025] In this case, the dielectric layer reliably increases the electric
field applied to the conductive liquid, so that the speed of movement of
the conductive fluid can be more easily improved.

[0026] In the above display device, the non-effective display region may
be defined by a light-shielding layer that is provided on one of the
first substrate and the second substrate, and the effective display
region may be defined by an aperture formed in the light-shielding layer.

[0027] In this case, the effective display region and the non-effective
display region can be properly and reliably defined with respect to the
display space.

[0028] An electric apparatus of the present invention includes a display
portion that displays information including characters and images. The
display portion includes any of the above display devices.

[0029] In the electric apparatus having the above configuration, the
display portion uses the display device that can improve the speed of
movement of the conductive liquid. Thus, a high-performance electric
apparatus capable of changing the display color in each of the pixel
regions at a high speed can be easily provided.

Effects of the Invention

[0030] The present invention can provide a display device that can improve
the speed of movement of the conductive liquid, and an electric apparatus
using the display device.

BRIEF DESCRIPTION OF DRAWINGS

[0031] FIG. 1 is plan view for explaining a display device and an image
display apparatus of Embodiment 1 of the present invention.

[0032] FIG. 2 is an enlarged plan view showing the main configuration of
the upper substrate in FIG. 1 when viewed from a display surface side.

[0033] FIG. 3 is an enlarged plan view showing the main configuration of
the lower substrate in FIG. 1 when viewed from a non-display surface
side.

[0034] FIGS. 4A and 4B are cross-sectional views showing the main
configuration of the display device in FIG. 1 during non-CF color display
and CF color display, respectively.

[0035] FIG. 5 is a diagram for explaining an operation example of the
image display apparatus.

[0036] FIG. 6 is a graph showing the average movement time of a conductive
liquid and the droplet coalescence probability of the conductive liquid
when a rib height is changed the display device.

[0037] FIG. 7 is an enlarged plan view showing the main configuration of a
lower substrate in a display device of Embodiment 2 of the present
invention when viewed from a non-display surface side.

[0038] FIGS. 8A and 8B are cross-sectional views showing the main
configuration of the display device in FIG. 7 during non-CF color display
and CF color display, respectively.

DESCRIPTION OF THE INVENTION

[0039] Hereinafter, preferred embodiments of a display device and an
electric apparatus of the present invention will be described with
reference to the drawings. In the following description, the present
invention is applied to an image display apparatus including a display
portion that can display color images. The size and size ratio of each of
the constituent members in the drawings do not exactly reflect those of
the actual constituent members.

Embodiment 1

[0040] FIG. 1 is a plan view for explaining a display device and an image
display apparatus of Embodiment 1 of the present invention. In FIG. 1, an
image display apparatus 1 of this embodiment includes a display portion
using a display device 10 of the present invention. The display portion
has a rectangular display surface. The display device 10 includes an
upper substrate 2 and a lower substrate 3 that are arranged to overlap
each other in the direction perpendicular to the sheet of FIG. 1. The
overlap between the upper substrate 2 and the lower substrate 3 forms an
effective display region of the display surface (as will be described in
detail later).

[0041] In the display device 10, a plurality of signal electrodes 4 are
spaced at predetermined intervals and arranged in stripes in the X
direction. Moreover, in the display device 10, a plurality of reference
electrodes 5 and a plurality of scanning electrodes 6 are alternately
arranged in stripes in the Y direction. The plurality of the signal
electrodes 4 intersect with the plurality of the reference electrodes 5
and the plurality of the scanning electrodes 6, and a plurality of pixel
regions are located at each of the intersections of the signal electrodes
4 and the scanning electrodes 6.

[0042] The signal electrodes 4, the reference electrodes 5, and the
scanning electrodes 6 are configured so that voltages can be
independently applied to these electrodes, and the voltages fall in a
predetermined voltage range between a High voltage (referred to as "H
voltage" in the following) that serves as a first voltage and a Low
voltage (referred to as "L voltage" in the following) that serves as a
second voltage (as will be described in detail later).

[0043] In the display device 10, the pixel regions are separated from one
another by ribs and provided in accordance with a plurality of colors
that enable full-color display to be shown on the display surface, as
will be described in detail later. The display device 10 changes the
display color on the display surface by moving a conductive liquid (as
will be described later) for each of a plurality of pixels (display
cells) arranged in a matrix using an electrowetting phenomenon.

[0044] One end of the signal electrodes 4, the reference electrodes 5, and
the scanning electrodes 6 are extended to the outside of the effective
display region of the display surface and form terminals 4a, 5a, and 6a,
respectively.

[0045] A signal driver 7 is connected to the individual terminals 4a of
the signal electrodes 4 via wires 7a. The signal driver 7 constitutes a
signal voltage application portion and applies a signal voltage Vd to
each of the signal electrodes 4 in accordance with information when the
image display apparatus 1 displays the information including characters
and images on the display surface.

[0046] A reference driver 8 is connected to the individual terminals 5a of
the reference electrodes 5 via wires 8a. The reference driver 8
constitutes a reference voltage application portion and applies a
reference voltage Vr to each of the reference electrodes 5 when the image
display apparatus 1 displays the information including characters and
images on the display surface.

[0047] A scanning driver 9 is connected to the individual terminals 6a of
the scanning electrodes 6 via wires 9a. The scanning driver 9 constitutes
a scanning voltage application portion and applies a scanning voltage Vs
to each of the scanning electrodes 6 when the image display apparatus 1
displays the information including characters and images on the display
surface.

[0048] The scanning driver 9 applies either a non-selected voltage or a
selected voltage to each of the scanning electrodes 6 as the scanning
voltage Vs. The non-selected voltage inhibits the movement of the
conductive liquid and the selected voltage allows the conductive liquid
to move in accordance with the signal voltage Vd. Moreover, the reference
driver 8 is operated with reference to the operation of the scanning
driver 9. The reference driver 8 applies either the non-selected voltage
that inhibits the movement of the conductive liquid or the selected
voltage that allows the conductive liquid to move in accordance with the
signal voltage Vd to each of the reference electrodes 5 as the reference
voltage Vr.

[0049] In the image display apparatus 1, the scanning driver 9 applies the
selected voltage to each of the scanning electrodes 6 in sequence, e.g.,
from the left to the right of FIG. 1, and the reference driver 8 applies
the selected voltage to each of the scanning electrodes 6 in sequence
from the left to the right of FIG. 1 in synchronization with the
operation of the scanning driver 9. Thus, the scanning driver 9 and the
reference driver 8 perform their respective scanning operations for each
line (as will be described in detail later).

[0050] The signal driver 7, the reference driver 8, and the scanning
driver 9 include a direct-current power supply or an alternating-current
power supply that supplies the signal voltage Vd, the reference voltage
Vr, and the scanning voltage Vs, respectively.

[0051] The reference driver 8 switches the polarity of the reference
voltage Vr at predetermined time intervals (e.g., 1 frame). Moreover, the
scanning driver 9 switches the polarity of the scanning voltage Vs in
accordance with the switching of the polarity of the reference voltage
Vr. Thus, since the polarities of the reference voltage Vr and the
scanning voltage Vs are switched at predetermined time intervals, the
localization of charges in the reference electrodes 5 and the scanning
electrodes 6 can be prevented, compared to the case where the voltages
with the same polarity are always applied to the reference electrodes 5
and the scanning electrodes 6. Moreover, it is possible to prevent the
adverse effects of a display failure (afterimage phenomenon) and low
reliability (a reduction in life) due to the localization of charges.

[0052] The pixel structure of the display device 10 will be described in
detail with reference to FIGS. 2 to 4 as well as FIG. 1.

[0053] FIG. 2 is an enlarged plan view showing the main configuration of
the upper substrate in FIG. 1 when viewed from the display surface side.
FIG. 3 is an enlarged plan view showing the main configuration of the
lower substrate in FIG. 1 when viewed from the non-display surface side.
FIGS. 4A and 4B are cross-sectional views showing the main configuration
of the display device in FIG. 1 during non-CF color display and CF color
display, respectively. For the sake of simplification, FIGS. 2 and 3 show
twelve pixels placed at the upper left corner of the plurality of pixels
on the display surface in FIG. 1.

[0054] In FIGS. 2 to 4, the display device 10 includes the upper substrate
2 that is provided on the display surface side and serves as a first
substrate, and the lower substrate 3 that is provided on the back (i.e.,
the non-display surface side) of the upper substrate 2 and serves as a
second substrate. In the display device 10, the upper substrate 2 and the
lower substrate 3 are located at a predetermined distance away from each
other, so that a predetermined display space S is formed between the
upper substrate 2 and the lower substrate 3. The conductive liquid 16 and
an insulating oil 17 that is not mixed with the conductive liquid 16 are
sealed in the display space S and can be moved in the X direction (the
lateral direction of FIG. 4). The conductive liquid 16 can be moved
toward an effective display region P1 or a non-effective display region
P2, as will be described later.

[0055] The conductive liquid 16 can be, e.g., an aqueous solution
including water as a solvent and a predetermined electrolyte as a solute.
Specifically, 1 mmol/L of potassium chloride (KCl) aqueous solution may
be used as the conductive liquid 16. Moreover, the conductive liquid 16
is colored black, e.g., with a self-dispersible pigment.

[0056] The conductive liquid 16 is colored black and therefore functions
as a shutter that allows or prevents light transmission. When the
conductive liquid 16 is slidably moved in the display space S toward the
reference electrode 5 (i.e., the effective display region P1) or the
scanning electrode 6 (i.e., the non-effective display region P2), the
display color of each pixel of the display device 10 is changed to black
or any color of RBG, as will be described in detail later.

[0057] The oil 17 can be, e.g., a nonpolar, colorless, and transparent oil
including one or more than one selected from a side-chain higher alcohol,
a side-chain higher fatty acid, an alkane hydrocarbon, a silicone oil,
and a matching oil. The oil 17 is shifted in the display space S as the
conductive liquid 16 is slidably moved.

[0058] The upper substrate 2 can be, e.g., a transparent glass material
such as a non-alkali glass substrate or a transparent sheet material such
as a transparent synthetic resin (e.g., an acrylic resin). A color filter
layer 11 and the signal electrodes 4 are formed in this order on the
surface of the upper substrate 2 that faces the non-display surface side.
Moreover, a hydrophobic film 12 is formed to cover the color filter layer
11 and the signal electrodes 4.

[0059] Like the upper substrate 2, the lower substrate 3 can be, e.g., a
transparent glass material such as a non-alkali glass substrate or a
transparent sheet material such as a transparent synthetic resin (e.g.,
an acrylic resin). The reference electrodes 5 and the scanning electrodes
6 are provided on the surface of the lower substrate 3 that faces the
display surface side. Moreover, a dielectric layer 13 is formed to cover
the reference electrodes 5 and the scanning electrodes 6. First rib
members 14a and second rib members 14b are formed parallel to the Y
direction and the X direction, respectively, on the surface of the
dielectric layer 13 that faces the display surface side. In the lower
substrate 3, a hydrophobic film 15 is further formed to cover the
dielectric layer 13 and the first and second rib members 14a, 14b.

[0060] A backlight 18 that emits, e.g., white illumination light is
integrally attached to the back (i.e., the non-display surface side) of
the lower substrate 3, thus providing a transmission type display device
10. The backlight 18 uses a light source such as a cold cathode
fluorescent tube or a LED.

[0061] The color filter layer 11 includes red (R), green (G), and blue (B)
color filters 11r, 11g, and 11b and a black matrix his serving as a
light-shielding layer, thereby constituting the pixels of R, G, and B
colors. In the color filter layer 11, as shown in FIG. 2, the R, G, and B
color filters 11r, 11g, and lib are successively arranged in columns in
the X direction, and each column includes four color filters in the Y
direction. Thus, a total of twelve pixels are arranged in three columns
(the X direction) and four rows (the Y direction).

[0062] As shown in FIG. 2, in each of the pixel regions P of the display
device 10, any of the R, G, and B color filters 11r, 11g, and lib is
provided in a portion corresponding to the effective display region P1
and the black matrix 11s is provided in a portion corresponding to the
non-effective display region P2 of the pixel. In other words, with
respect to the display space S, the non-effective display region
(non-aperture region) P2 is defined by the black matrix (light-shielding
layer) 11s and the effective display region P1 is defined by an aperture
(i.e., any of the color filters 11r, 11g, and 11b) formed in that black
matrix 11s.

[0063] In the display device 10, the area of each of the color filters
11r, 11g, and 11b is the same as or slightly larger than that of the
effective display region P1. On the other hand, the area of the black
matrix 11s is the same as or slightly smaller than that of the
non-effective display region P2. In FIG. 2, the boundary between two
black matrixes 11s corresponding to the adjacent pixels is indicated by a
dotted line to clarify the boundary between the adjacent pixels.
Actually, however, no boundary is present between the black matrixes 11s
of the color filter layer 11.

[0064] In the display device 10, the inside of the display space S is
divided into the pixel regions P by the ribs 14 that serve as partitions
and have the first rib members 14a and the second rib members 14b. As
shown in FIG. 3, in the display device 10, the inside of the display
space S of each pixel is partitioned by the ribs 14 that are in the form
of a frame so as to surround the corresponding pixel region R
Specifically, the inside of the display space S of each pixel is
partitioned by the frame-shaped ribs composed of two first rib members
14a formed parallel to the Y direction (i.e., the direction perpendicular
to the direction of movement of the conductive liquid 16) and two first
rib members 14b formed parallel to the X direction (i.e., the direction
parallel to the direction of movement of the conductive liquid 16).

[0065] The first and second rib members 14a, 14b of the ribs 14 are made
of, e.g., an epoxy resin resist material.

[0066] As shown in FIG. 4, a height h of the first and second rib members
14a, 14b in the direction perpendicular to the upper substrate 2 and the
lower substrate 3 (i.e., the longitudinal direction of FIG. 4) is set so
as to satisfy the following inequalities (1) and (2) using a gap size H
of the display space S in the above perpendicular direction.

height h.ltoreq.0.9.times.(gap size H) (1)

0.65.times.(gap size H).ltoreq.height h (2)

[0067] In other words, the height h of the first and second rib members
14a, 14b, i.e., the height by which the first and second rib members 14a,
14b protrude from the dielectric layer 13 is determined using the gap
size H of the display space S, i.e., the distance between the hydrophobic
film 12 and the hydrophobic film 15. By setting the height h of the ribs
14 in this manner, the speed of movement of the conductive liquid 16 can
be improved while preventing the flow of the conductive liquid 16 between
the adjacent pixels.

[0068] Specifically, setting the height h to satisfy the inequality (1)
can improve the speed of movement of the conductive liquid 16. Moreover,
setting the height h to satisfy the inequality (2) can reliably prevent
the conductive liquid 16 from entering the adjacent pixel regions P when
the conductive liquid 16 is moved.

[0069] If the height his larger than 0.9.times.(gap size H), it is
difficult to improve the speed of movement of the conductive liquid 16.
If the height h is smaller than 0.65.times.(gap height H), there is a
risk that the conductive liquid 16 will enter the adjacent pixel regions
P when the conductive liquid 16 is moved.

[0070] A specific gap size H is, e.g., 0.2 mm, and a specific height his
0.13 mm to 0.18 mm. Further, the gap size H is maintained at a
predetermined size by the use of a sealing material (not shown) that is
provided on the periphery of the display portion.

[0071] The hydrophobic films 12, 15 are made of, e.g., a transparent
synthetic resin, and preferably a fluoro polymer that functions as a
hydrophilic layer for the conductive liquid 16 when a voltage is applied.
This can significantly change the wettability (contact angle) between the
conductive liquid 16 and each of the surfaces of the upper and lower
substrates 2, 3 that face the display space S. Thus, the speed of
movement of the conductive liquid 16 can be improved. The dielectric
layer 13 can be, e.g., a transparent dielectric film containing parylene,
a silicon nitride, a hafnium oxide, a zinc oxide, a titanium dioxide, or
an aluminum oxide. A specific thickness of each of the hydrophobic films
12, 15 ranges from several hundred nanometers to several micrometers. A
specific thickness of the dielectric layer 13 is several hundred
nanometers. The hydrophobic film 12 does not electrically insulate the
signal electrodes 4 from the conductive liquid 16, and therefore not
interfere with the improvement in responsibility of the conductive liquid
16.

[0072] The reference electrodes 5 and the scanning electrodes 6 are made
of, e.g., transparent electrode materials such as indium oxides (ITO),
tin oxides (SnO.sub.2), and zinc oxides (AZO, GZO, or IZO). The reference
electrodes 5 and the scanning electrodes 6 are formed in stripes on the
lower substrate 3 by a known film forming method such as sputtering.

[0073] The signal electrodes 4 can be, e.g., linear wiring that is
arranged parallel to the X direction. The signal electrodes 4 are placed
on the color filter layer 11 so as to extend substantially through the
center of each of the pixel regions P in the Y direction, and further to
come into electrical contact with the conductive liquid 16 via the
hydrophobic film 12. This can improve the responsibility of the
conductive liquid 16 during a display operation.

[0074] A material that is electrochemically inert to the conductive liquid
16 is used for the signal electrodes 4. Therefore, even if the signal
voltage Vd (e.g., 40 V) is applied to the signal electrodes 4, the
electrochemical reaction between the signal electrodes 4 and the
conductive liquid 16 can be minimized. Thus, it is possible to prevent
electrolysis of the signal electrodes 4 and to improve the reliability
and life of the display device 10.

[0075] Specifically, the signal electrodes 4 are made of, e.g., an
electrode material including at least one of gold, silver, copper,
platinum, and palladium. The signal electrodes 4 may be formed by fixing
thin wires made of the above metal material on the color filter layer 11
or by mounting an ink material such as a conductive paste containing the
metal material on the color filter layer 11 with screen printing or the
like.

[0076] The shape of the signal electrode 4 is determined using the
transmittance of the reference electrode 5 located below the effective
display region P1 of the pixel. Specifically, based on a transmittance of
about 75% to 95% of the reference electrode 5, the shape of the signal
electrode 4 is determined so that the occupation area of the signal
electrode 4 on the effective display region P1 is 30% or less, preferably
10% or less, and more preferably 5% or less of the area of the effective
display region P1.

[0077] In each pixel of the display device 10 having the above
configuration, as shown in FIG. 4A, when the conductive liquid 16 is held
between the color filter 11r and the reference electrode 5, light from
the backlight 18 is blocked by the conductive liquid 16, so that the
black display (non-CF color display) is performed. On the other hand, as
shown in FIG. 4B, when the conductive liquid 16 is held between the black
matrix 11s and the scanning electrode 6, light from the backlight 18 is
not blocked by the conductive liquid 16 and passes through the color
filter 11r, so that the red display (CF color display) is performed.

[0078] Hereinafter, a display operation of the image display apparatus 1
of this embodiment having the above configuration will be described in
detail with reference to FIG. 5 as well as FIGS. 1 to 4.

[0079] FIG. 5 is a diagram for explaining an operation example of the
image display apparatus 1.

[0080] In FIG. 5, the reference driver 8 and the scanning driver 9 apply
the selected voltages (i.e., the reference voltage Vr and the scanning
voltage Vs) to the reference electrodes 5 and the scanning electrodes 6
in sequence in a predetermined scanning direction, e.g., from the left to
the right of FIG. 5, respectively. Specifically, the reference driver 8
and the scanning driver 9 perform their scanning operations to determine
a selected line by applying the H voltage (first voltage) and the L
voltage (second voltage) as the selected voltages to the reference
electrodes 5 and the scanning electrodes 6 in sequence, respectively. In
this selected line, the signal driver 7 applies the H or L voltage (i.e.,
the signal voltage Vd) to the corresponding signal electrodes 4 in
accordance with the external image input signal. Thus, in each of the
pixels of the selected line, the conductive liquid 16 is moved toward the
effective display region P1 or the non-effective display region P2, and
the display color on the display surface is changed accordingly.

[0081] On the other hand, the reference driver 8 and the scanning driver 9
apply the non-selected voltages (i.e., the reference voltage Vr and the
scanning voltage Vs) to non-selected lines, namely to all the remaining
reference electrodes 5 and scanning electrodes 6, respectively.
Specifically, the reference driver 8 and the scanning driver 9 apply,
e.g., intermediate voltages (Middle voltages, referred to as "M voltages"
in the following) between the H voltage and the L voltage as the
non-selected voltages to all the remaining reference electrodes 5 and
scanning electrodes 6, respectively. Thus, in each of the pixels of the
non-selected lines, the conductive liquid 16 stands still without
unnecessary displacement from the effective display region P1 or the
non-effective display region P2, and the display color on the display
surface is unchanged.

[0082] Table 1 shows the combinations of the voltages applied to the
reference electrodes 5, the scanning electrodes 6, and the signal
electrodes 4 in the above display operation. As shown in Table 1, the
behavior of the conductive liquid 16 and the display color on the display
surface depend on the applied voltages. In Table 1, the H voltage, the L
voltage, and the M voltage are abbreviated to "H", "L", and "M",
respectively (the same is true for Table 2 in the following). The
specific values of the H voltage, the L voltage, and the M voltage are,
e.g., +16 V, 0 V, and +8 V, respectively.

[0084] In the selected line, e.g., when the H voltage is applied to the
signal electrodes 4, there is no potential difference between the
reference electrode 5 and the signal electrodes 4 because the H voltage
is applied to both of these electrodes. On the other hand, a potential
difference between the signal electrodes 4 and the scanning electrode 6
occurs because the L voltage is applied to the scanning electrode 6.
Therefore, the conductive liquid 16 is moved in the display space S
toward the scanning electrode 6 that makes a potential difference from
the signal electrodes 4. Consequently, the conductive liquid 16 has been
moved toward the non-effective display region P2, as shown in FIG. 4B,
and allows the illumination light emitted from the backlight 18 to reach
the color filter 11r by shifting the oil 17 toward the reference
electrode 5. Thus, the display color on the display surface becomes red
display (i.e., the CF color display) due to the color filter 11r. In the
image display apparatus 1, when the CF color display is performed in all
the three adjacent R, G, and B pixels as a result of the movement of the
conductive liquid 16 toward the non-effective display region P2, the red,
green, and blue colors of light from the corresponding R, G, and B pixels
are mixed into white light, resulting in the white display.

[0085] In the selected line, when the L voltage is applied to the signal
electrodes 4, a potential difference occurs between the reference
electrode 5 and the signal electrodes 4, but not between the signal
electrodes 4 and the scanning electrode 6. Therefore, the conductive
liquid 16 is moved in the display space S toward the reference electrode
5 that makes a potential difference from the signal electrodes 4.
Consequently, the conductive liquid 16 has been moved toward the
effective display region P1, as shown in FIG. 4A, and prevents the
illumination light emitted from the backlight 18 from reaching the color
filter 11r. Thus, the display color on the display surface becomes black
display (i.e., the non-CF color display) due to the presence of the
conductive liquid 16.

[0086] <Non-selected line operation>

[0087] In the non-selected lines, e.g., when the H voltage is applied to
the signal electrodes 4, the conductive liquid 16 stands still in the
same position, and the current display color is maintained. Since the M
voltages are applied to both the reference electrodes 5 and the scanning
electrodes 6, the potential difference between the reference electrodes 5
and the signal electrodes 4 is the same as that between the scanning
electrodes 6 and the signal electrodes 4. Consequently, the display color
is maintained without changing from the black display or the CF color
display in the current state.

[0088] Similarly, in the non-selected lines, even when the L voltage is
applied to the signal electrodes 4, the conductive liquid 16 stands still
in the same position, and the current display color is maintained. Since
the M voltages are applied to both the reference electrodes 5 and the
scanning electrodes 6, the potential difference between the reference
electrodes 5 and the signal electrodes 4 is the same as that between the
scanning electrodes 6 and the signal electrodes 4.

[0089] As described above, in the non-selected lines, the conductive
liquid 16 is not moved, but stands still and the display color on the
display surface is unchanged regardless of whether the H or L voltage is
applied to the signal electrodes 4.

[0090] On the other hand, in the selected line, the conductive liquid 16
can be moved in accordance with the voltage applied to the signal
electrodes 4, as described above, and the display color on the display
surface can be changed accordingly.

[0091] In the image display apparatus 1, depending on the combinations of
the applied voltages in Table 1, the display color of each pixel on the
selected line can be, e.g., the CF colors (red, green, or blue) produced
by the color filters 11r, 11g, and 11b or the non-CF color (black) due to
the conductive liquid 16 in accordance with the voltage applied to the
signal electrodes 4 corresponding to the individual pixels, as shown in
FIG. 5. When the reference driver 8 and the scanning driver 9 determine a
selected line of the reference electrode 5 and the scanning electrode 6
by performing their scanning operations, e.g., from the left to the right
of FIG. 5, the display colors of the pixels in the display portion of the
image display apparatus 1 also are changed in sequence from the left to
the right of FIG. 5. Therefore, if the reference driver 8 and the
scanning driver 9 perform the scanning operations at a high speed, the
display colors of the pixels in the display portion of the image display
apparatus 1 also can be changed at a high speed. Moreover, by applying
the signal voltage Vd to the signal electrodes 4 in synchronization with
the scanning operation for the selected line, the image display apparatus
1 can display various information including dynamic images based on the
external image input signal.

[0092] The combinations of the voltages applied to the reference
electrodes 5, the scanning electrodes 6, and the signal electrodes 4 are
not limited to Table 1, and may be as shown in Table 2.

[0093] The reference driver 8 and the scanning driver 9 perform their
scanning operations to determine a selected line by applying the L
voltage (second voltage) and the H voltage (first voltage) as the
selected voltages to the reference electrodes 5 and the scanning
electrodes 6 in sequence in a predetermined scanning direction, e.g.,
from the left to the right of FIG. 5, respectively. In this selected
line, the signal driver 7 applies the H or L voltage (i.e., the signal
voltage Vd) to the corresponding signal electrodes 4 in accordance with
the external image input signal.

[0094] On the other hand, the reference driver 8 and the scanning driver 9
apply the M voltages as the non-selected voltages to the non-selected
lines, namely to all the remaining reference electrodes 5 and scanning
electrodes 6.

[0095] <Selected Line Operation>

[0096] In the selected line, e.g., when the L voltage is applied to the
signal electrodes 4, there is no potential difference between the
reference electrode 5 and the signal electrodes 4 because the L voltage
is applied to both of these electrodes. On the other hand, a potential
difference between the signal electrodes 4 and the scanning electrode 6
occurs because the H voltage is applied to the scanning electrode 6.
Therefore, the conductive liquid 16 is moved in the display space S
toward the scanning electrode 6 that makes a potential difference from
the signal electrodes 4. Consequently, the conductive liquid 16 has been
moved toward the non-effective display region P2, as shown in FIG. 4B,
and allows the illumination light emitted from the backlight 18 to reach
the color filter 11r by shifting the oil 17 toward the reference
electrode 5. Thus, the display color on the display surface becomes red
display (i.e., the CF color display) due to the color filter 11r. Like
Table 1, when the CF color display is performed in all the three adjacent
R, G, and B pixels, the white display is performed.

[0097] In the selected line, when the H voltage is applied to the signal
electrodes 4, a potential difference occurs between the reference
electrode 5 and the signal electrodes 4, but not between the signal
electrodes 4 and the scanning electrode 6. Therefore, the conductive
liquid 16 is moved in the display space S toward the reference electrode
that makes a potential difference from the signal electrodes 4.
Consequently, the conductive liquid 16 has been moved toward the
effective display region P1, as shown in FIG. 4A, and prevents the
illumination light emitted from the backlight 18 from reaching the color
filter 11r. Thus, the display color on the display surface becomes black
display (i.e., the non-CF color display) due to the presence of the
conductive liquid 16.

[0098] <Non-Selected Line Operation>

[0099] In the non-selected lines, e.g., when the L voltage is applied to
the signal electrodes 4, the conductive liquid 16 stands still in the
same position, and the current display color is maintained. Since the M
voltages are applied to both the reference electrodes 5 and the scanning
electrodes 6, the potential difference between the reference electrodes 5
and the signal electrodes 4 is the same as that between the scanning
electrodes 6 and the signal electrodes 4. Consequently, the display color
is maintained without changing from the black display or the CF color
display in the current state.

[0100] Similarly, in the non-selected lines, even when the H voltage is
applied to the signal electrodes 4, the conductive liquid 16 stands still
in the same position, and the current display color is maintained. Since
the M voltages are applied to both the reference electrodes 5 and the
scanning electrodes 6, the potential difference between the reference
electrodes 5 and the signal electrodes 4 is the same as that between the
scanning electrodes 6 and the signal electrodes 4.

[0101] In the non-selected lines, as shown in Table 2, similarly to Table
1, the conductive liquid 16 is not moved, but stands still and the
display color on the display surface is unchanged regardless of whether
the H or L voltage is applied to the signal electrodes 4.

[0102] On the other hand, in the selected line, the conductive liquid 16
can be moved in accordance with the voltage applied to the signal
electrodes 4, as described above, and the display color on the display
surface can be changed accordingly.

[0103] In the image display apparatus 1 of this embodiment, other than the
combinations of the applied voltages shown in Tables 1 and 2, the voltage
applied to the signal electrodes 4 not only has two values of the H
voltage and the L voltage, but also may be changed between the H voltage
and the L voltage in accordance with information to be displayed on the
display surface. That is, the image display apparatus 1 can perform the
gradation display by controlling the signal voltage Vd. Thus, the display
device 10 can achieve excellent display performance.

[0104] In the display device 10 of this embodiment having the above
configuration, the ribs 14 are provided in the form of a frame so as to
surround the corresponding pixel region P. Moreover, in the display
device 10 of this embodiment, the height h of the ribs 14 is set so as to
satisfy the inequality (1) and to be smaller than the gap size H of the
display space S in the perpendicular direction. Thus, unlike the
conventional example, a clearance can be created between the upper
substrate (i.e., the other of the first and second substrates) 2 and the
ribs 14 in the display device 10 of this embodiment, so that the speed of
movement of the conductive liquid 16 can be reliably improved.

[0105] In the display device 10 of this embodiment, the height h of the
ribs 14 is set so as to satisfy the inequality (2). Therefore, it is
possible to reliably prevent the conductive liquid 16 from entering the
adjacent pixel regions P when the conductive liquid 16 is moved. Thus, in
this embodiment, even if the speed of movement of the conductive liquid
16 is improved so that the speed of change of the display color is
increased, a high-performance display device 10 that does not reduce the
display quality can be easily provided.

[0106] Hereinafter, the results of verification tests conducted by the
present inventors will be described in detail with reference to FIG. 6.

[0107] FIG. 6. is a graph showing the average movement time of the
conductive liquid and the droplet coalescence probability of the
conductive liquid when the rib height of the display device is changed.

[0108] Referring to FIG. 6, samples having 9.times.9 pixel regions P were
prepared for the verification tests, and the average movement time and
the droplet coalescence probability of the conductive liquid 16 were
determined when the height h of the ribs 14 was changed with respect to
the gap size H. In this case, the average movement time of the conductive
liquid 16 indicates the average of the time required for the conductive
liquid 16 to move from the effective display region P1 to the
non-effective display region P2 or to move from the non-effective display
region P2 to the effective display region P1. The droplet coalescence
probability of the conductive liquid 16 indicates the probability of the
conductive liquid 16 entering the adjacent pixel regions P when the
conductive liquid 16 is moved.

[0109] As represented by a graph 50 in FIG. 6, if the height h of the ribs
14 was not more than 0.9.times.(gap size H), the speed of movement of the
conductive liquid 16 was improved. On the other hand, if the height h of
the ribs 14 was more than 0.9.times.(gap size H), it was demonstrated
that the speed of movement of the conductive liquid 16 was significantly
reduced and not easily improved.

[0110] As represented by graph 60 in FIG. 6, if the height h of the ribs
14 was not less than 0.65.times.(gap size it was confirmed that the
conductive liquid 16 did not enter the adjacent pixel regions P at all
when the conductive liquid 16 was moved. On the other hand, if the height
h of the ribs 14 was less than 0.65.times.(gap size R), it was
demonstrated that the conductive liquid 16 was likely to enter the
adjacent pixel regions P when the conductive liquid 16 was moved, and
there was a risk that the display quality would be reduced.

[0111] In the image display apparatus (electric apparatus) 1 of this
embodiment, the display device 10 is used in the display portion.
Therefore, a high-performance pixel display apparatus (electric
apparatus) 1 capable of changing the display color in each of the pixel
regions P at a high speed can be easily provided.

[0112] In the display device 10 of this embodiment, the signal driver
(signal voltage application portion) 7, the reference driver (reference
voltage application portion) 8, and the scanning driver (scanning voltage
application portion) 9 apply the signal voltage Vd, the reference voltage
Vr, and the scanning voltage Vs to the signal electrodes 4, the reference
electrodes 5, and the scanning electrodes 6, respectively. Thus, in this
embodiment, a matrix-driven display device 10 with excellent display
quality can be easily provided, and the display color in each of the
pixel regions can be appropriately changed.

Embodiment 2

[0113] FIG. 7 is an enlarged plan view showing the main configuration of a
lower substrate in a display device of Embodiment 2 of the present
invention when viewed from a non-display surface side. FIGS. 8A and 8B
are cross-sectional views showing the main configuration of the display
device in FIG. 7 during non-CF color display and CF color display,
respectively. In FIGS. 7, 8A, and 8B, this embodiment mainly differs from
Embodiment 1 in that clearances through which the adjacent pixel regions
can communicate with each other are formed between each of the ends of
the first and second rib members. The same components as those of
Embodiment 1 are denoted by the same reference numerals, and the
explanation will not be repeated.

[0114] As shown in FIGS. 7, 8A, and 8B, in a display device 10 of this
embodiment, the inside of the display space S of each pixel is
partitioned by two first rib members 14a' formed parallel to the Y
direction (i.e., the direction perpendicular to the direction of movement
of the conductive liquid 16) and two first rib members 14b' formed
parallel to the X direction (i.e., the direction parallel to the
direction of movement of the conductive liquid 16).

[0115] In other words, clearances K are formed between each of the ends of
the first and second rib members 14a', 14b' in the display device 10 of
this embodiment. The adjacent pixel regions P can communicate with each
other through these clearances K. In the display device 10 of this
embodiment, the clearances K are provided in four corners of each of the
pixel regions P, in addition to the clearance between the upper substrate
2 and the first and second rib members 14a', 14b'. This allows the
conductive liquid 16 to move smoothly.

[0116] With the above configuration, this embodiment can have effects
comparable to those of Embodiment 1. In this embodiment, since the
clearances K are formed between each of the ends of the first and second
rib members 14a', 14b', the clearances K are provided in four corners of
each of the pixel regions P. Due to the presence of these clearances K,
the conductive liquid 16 can be moved smoothly, and thus the speed of
movement of the conductive liquid 16 can be improved.

[0117] In the above description, the clearances K are provided in four
corners of each of the pixel regions P. However, this embodiment is not
limited thereto, as long as clearances are formed with respect to the
ribs 14 so that the adjacent pixel regions P can communicate with each
other. Specifically, e.g., clearances may be formed in the center portion
of the second rib members 14b' in each of the pixel regions P.

[0118] It should be noted that the above embodiments are all illustrative
and not restrictive. The technological scope of the present invention is
defined by the appended claims, and all changes that come within the
range of equivalency of the claims are intended to be embraced therein.

[0119] For example, in the above description, the present invention is
applied to an image display apparatus including a display portion that
can display color images. However, the present invention is not limited
thereto, as long as it is applied to an electric apparatus with a display
portion that displays the information including characters and images.
For example, the present invention is suitable for various electric
apparatuses with display portions such as a personal digital assistant
such as an electronic organizer, a display apparatus for a personal
computer or television, and an electronic paper.

[0120] In the above description, the electrowetting-type display device is
used, in which the conductive liquid is moved in accordance with the
application of an electric field to the conductive liquid. However, the
display device of the present invention is not limited thereto, as long
as it is an electric-field-induced display device that can change the
display color on the display surface by moving the conductive liquid in
the display space with the use of an external electric field. For
example, the present invention can be applied to other types of
electric-field-induced display devices such as an electroosmotic type, an
electrophoretic type, and a dielectrophoretic type.

[0121] As described in each of the above embodiments, the
electrowetting-type display device is preferred because the conductive
liquid can be moved at a high speed and a low drive voltage. Moreover,
since three different electrodes are used to move the conductive liquid
slidably, the electrowetting-type display device can achieve both a high
switching speed of the display color on the display surface and electric
power saving more easily than the display device in which the shape of
the conductive liquid is changed. In the electrowetting-type display
device, the display color is changed with the movement of the conductive
liquid. Therefore, unlike a liquid crystal display apparatus or the like,
there is no viewing angle dependence. Moreover, since a switching device
does not need to be provided for each pixel, a high-performance
matrix-driven display device having a simple structure can be achieved at
a low cost. Further, the electrowetting-type display device does not use
a birefringent material such as a liquid crystal layer. Therefore, it is
possible to easily provide a high brightness display device with
excellent utilization efficiency of light from the backlight or ambient
light used for information display.

[0122] In the above description, the height h of the ribs is set so as to
satisfy the inequalities (1) and (2). However, the ribs of the present
invention are not limited thereto, as long as the height h of the ribs is
set to be smaller than the gap size H of the display space in the
perpendicular direction. In other words, the height h of the ribs of the
present invention can be appropriately changed to a size less than the
gap size H in accordance with the properties of the conductive liquid
such as viscosity, the size of the pixel region, or the magnitude of the
voltages applied to the signal electrodes, the reference electrodes, and
the scanning electrodes.

[0123] In the above description, the ribs are provided on the lower
substrate (second substrate). However, the ribs of the present invention
are not limited thereto, as long as the ribs are provided on one of the
upper substrate (first substrate) and the lower substrate (second
substrate) so as to partition the inside of the display space in
accordance with each of the pixel regions. That is, the ribs may be
provided on the first substrate on the display surface side.

[0124] The above description refers to the transmission type display
device including a backlight. However, the present invention is not
limited thereto, and may be applied to a reflection type display device
including a light reflection portion such as a diffuse reflection plate,
a semi-transmission type display device including the light reflection
portion along with a backlight, or the like.

[0125] In the above description, the signal electrodes are provided on the
upper substrate (first substrate) and the reference electrodes and the
scanning electrodes are provided on the lower substrate (second
substrate). However, the present invention is not limited thereto, and
may have a configuration in which the signal electrodes are placed in the
display space so as to come into contact with the conductive liquid, and
the reference electrodes and the scanning electrodes are provided on one
of the first substrate and the second substrate so as to be electrically
insulated from the conductive liquid and each other. Specifically, e.g.,
the signal electrodes may be provided on the second substrate or on the
ribs, and the reference electrodes and the scanning electrodes may be
provided on the first substrate.

[0126] In the above description, the reference electrodes and the scanning
electrodes are located on the effective display region side and the
non-effective display region side, respectively. However, the present
invention is not limited thereto, and the reference electrodes and the
scanning electrodes may be located on the non-effective display region
side and the effective display region side, respectively.

[0127] In the above description, the reference electrodes and the scanning
electrodes are provided on the surface of the lower substrate (second
substrate) that faces the display surface side. However, the present
invention is not limited thereto, and can use the reference electrodes
and the scanning electrodes that are buried in the second substrate made
of an insulating material. In this case, the second substrate also can
serve as a dielectric layer, which can eliminate the formation of the
dielectric layer. Moreover, the signal electrodes may be directly
provided on the first and second substrates serving as dielectric layers,
and thus may be placed in the display space.

[0128] In the above description, the reference electrodes and the scanning
electrodes are made of transparent electrode materials. However, the
present invention is not limited thereto, as long as either one of the
reference electrodes and the scanning electrodes, which are arranged to
face the effective display regions of the pixels, are made of the
transparent electrode materials. The other electrodes that do not face
the effective display regions can be made of opaque electrode materials
such as aluminum, silver, chromium, and other metals.

[0129] In the above description, the reference electrodes and the scanning
electrodes are in the form of stripes. However, the shapes of the
reference electrodes and the scanning electrodes of the present invention
are not limited thereto. For example, the reflection type display device
may use linear or mesh electrodes that are not likely to cause a light
loss, since the utilization efficiency of light used for information
display is lower in the reflection type display device than in the
transmission type display device.

[0130] In the above description, the signal electrodes are linear wiring.
However, the signal electrodes of the present invention are not limited
thereto, and can be wiring with other shapes such as mesh wiring.

[0131] As described in each of the above embodiments, it is preferable
that the shape of the signal electrodes is determined using the
transmittance of the reference electrodes and the scanning electrodes
that are transparent electrodes. This is because even if the signal
electrodes are made of an opaque material, shadows of the signal
electrodes can be prevented from appearing on the display surface, and
thus a decrease in display quality can be suppressed. The use of the
linear wiring is more preferred because the decrease in display quality
can be reliably suppressed.

[0132] In the above description, the conductive liquid is a potassium
chloride aqueous solution, and the signal electrodes include at least one
of gold, silver, copper, platinum, and palladium. However, the present
invention is not limited thereto, as long as a material that is
electrochemically inert to the conductive liquid is used for the signal
electrodes that are placed in the display space and come into contact
with the conductive liquid. Specifically, the conductive liquid can be,
e.g., a material including an electrolyte such as a zinc chloride,
potassium hydroxide, sodium hydroxide, alkali metal hydroxide, zinc
oxide, sodium chloride, lithium salt, phosphoric acid, alkali metal
carbonate, or ceramics with oxygen ion conductivity. The solvent can be,
e.g., an organic solvent such as alcohol, acetone, formamide, or ethylene
glycol other than water. The conductive liquid of the present invention
also can be an ionic liquid (room temperature molten salt) including
pyridine-, alicyclic amine-, or aliphatic amine-based cations and
fluorine anions such as fluoride ions or triflate.

[0133] As described in each of the above embodiments, the aqueous solution
in which a predetermined electrolyte is dissolved is preferred for the
conductive liquid because the display device can have excellent handling
properties and also be easily produced.

[0134] The signal electrodes of the present invention may be in the
passive state including an electrode body composed of a conductive metal
such as aluminum, nickel, iron, cobalt, chromium, titanium, tantalum,
niobium, or an alloy thereof and an oxide film disposed to cover the
surface of the electrode body.

[0135] As described in each of the above embodiments, the signal
electrodes including at least one of gold, silver, copper, platinum, and
palladium are preferred because these metals have a low ionization
tendency and make it possible not only to simplify the signal electrodes,
but also to reliably prevent an electrochemical reaction between the
signal electrodes and the conductive liquid. Thus, the display device can
easily prevent a reduction in the reliability and have a long life.
Moreover, with the use of the metals having a low ionization tendency,
the interfacial tension at the interface between the signal electrodes
and the conductive liquid can be relatively small. Therefore, when the
conductive liquid is not moved, it can be easily held in a stable state
at the fixed position.

[0136] In the above description, the nonpolar oil is used. However, the
present invention is not limited thereto, as long as an insulating fluid
that is not mixed with the conductive liquid is used. For example, air
may be used instead of the oil. Moreover, silicone oil or an aliphatic
hydrocarbon also can be used as the oil.

[0137] As described in each of the above embodiments, the nonpolar oil
that is not compatible with the conductive liquid is preferred because
the droplets of the conductive liquid move more easily in the nonpolar
oil compared to the use of air and the conductive liquid. Consequently,
the conductive liquid can be moved at a high speed, and the display color
can be switched at a high speed.

[0138] In the above description, the black colored conductive liquid and
the color filter layer are used to form the pixels of R, G, and B colors
on the display surface side. However, the present invention is not
limited thereto, as long as a plurality of pixel regions are provided in
accordance with a plurality of colors that enable full-color display to
be shown on the display surface. Specifically, the conductive liquids
with different colors such as RGB, CMY composed of cyan (C), magenta (M),
and yellow (Y), or RGBYC also can be used.

[0139] In the above description, the color filter layer is formed on the
surface of the upper substrate (first substrate) that faces the
non-display surface side. However, the present invention is not limited
thereto, and the color filter layer may be formed on the surface of the
first substrate that faces the display surface side or on the lower
substrate (second substrate). Thus, the color filter layer is preferred
compared to the use of the conductive liquids with different colors
because the display device can be easily produced. Moreover, the color
filter layer is also preferred because the effective display region and
the non-effective display region can be properly and reliably defined
with respect to the display space by the color filter (aperture) and the
black matrix (light-shielding layer) included in the color filter layer,
respectively.

INDUSTRIAL APPLICABILITY

[0140] The present invention is useful for a display device that can
improve the speed of movement of a conductive liquid, and an electric
apparatus using the display device.